linux-kernel - Re: [RFC] strcpys(): New function for copying strings safely

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Date:   Sun, 27 Jun 2021 21:46:38 +0200
From:   "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
To:     glibc <libc-alpha@...rceware.org>
Cc:     tech@...nbsd.org, Christoph Hellwig <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] strcpys(): New function for copying strings safely

On 6/27/21 9:26 PM, Alejandro Colomar (man-pages) wrote:
> 
> It is designed so that usage requires the minimum number of lines of 
> code for complete usage (including error handling checks):
> 
> [[
> // When we already checked that 'size' is >= 1
> // and truncation is not an issue:
> 
> strcpys_np(size, dest, src, NULL);

Also, given how unlikely this case is, I have in my code:
`[[gnu::warn_unused_result]]`

I forgot to talk about it in the definition I sent.  I would put that 
attribute in the glibc definition, if this is added to glibc.

To ignore it, a simple cast of the result to `(void)` should be enough 
(or a more complex macro, like `UNUSED(strcpys_np(...));`).
> 
> [[
> 
> #include <string.h>
> #include <sys/types.h>
> 
> 
> [[gnu::nonnull]]
> ssize_t strscpy_np(ssize_t size,
>                     char dest[static restrict size],
>                     const char src[static restrict size])
> {
>      ssize_t len;
> 
>      if (size <= 0)
>          return -1;
> 
>      len = strnlen(src, size - 1);
>      memcpy(dest, src, len);
>      dest[len] = '\0';
> 
>      return len;
> }
> 
> [[gnu::nonnull(2, 3)]]
[[gnu::warn_unused_result]]
> int strcpys_np(ssize_t size,
>                 char dest[static restrict size],
>                 const char src[static restrict size],
>                 ssize_t *restrict len)
> {
>      ssize_t l;
> 
>      l = strscpy_np(size, dest, src);
>      if (len)
>          *len = l;
> 
>      if (l == -1)
>          return -1;
>      if (l >= size)
>          return 1;
>      return 0;
> }
> 
> ]]

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/